Priority is claimed on Japanese Patent Application No. 2009-103075, filed on Apr. 21, 2009, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle gradient estimating device and a vehicle traveling control device.
2. Description of the Related Art
Heretofore, there has been known a road gradient estimating device including an acceleration sensor for detecting an acceleration acting on a vehicle in the horizontal direction and an actual acceleration sensor for calculating an acceleration from a variation in the speed of a vehicle, and estimating a road surface gradient of a road being traveled on the basis of a difference between an output of the actual acceleration sensor and an output of the acceleration sensor reflecting an acceleration of gravity due to the road surface gradient of the road being traveled (for example, refer to Japanese Unexamined Patent Application, First Publication No. H11-351864).
In addition, for some time, there has been known the following traveling control device for detecting a road surface gradient of a road being traveled from a predetermined road surface gradient characteristic with respect to a brake pressure on the basis of a brake pressure obtained when a vehicle started to move by gradually decreasing the brake pressure in a vehicle stop state (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2005-035347).
However, in the road gradient estimating device according to the related art, since the road surface gradient is estimated on the basis of the output of the acceleration sensor mounted to the vehicle, when a difference arises in a mounting angle of the acceleration sensor, there is a problem in that an estimation error of the road surface gradient increases. In addition, even when an offset of an output increases due to a variation in timing of the acceleration sensor, there is a problem in that the estimation error of the road surface gradient increases.
In addition, since it is difficult to automatically correct the estimation error of the road surface gradient caused by the acceleration sensor when the vehicle travels or stops, there is a problem in that an inappropriate traveling control is performed due to a road surface gradient having a large estimation error.
When a downhill is estimated as a flat road, there is a problem in that a subject vehicle inappropriately moves forward to be excessively close to a preceding vehicle. In addition, when a flat road is estimated as an uphill or a downhill, there is a problem in that a starting driving force or a stopping braking force becomes excessively large or small. However, in this case, when an appropriate distance between a forward object and the subject vehicle is ensured by a driver in addition to a feedback control of a driving force or a braking force, or an output of a distance sensor for detecting a distance between the forward object such as a preceding vehicle and the subject vehicle, it is possible to appropriately control a traveling state of the subject vehicle so as to prevent a collision between the subject vehicle and the object existing in front of the subject vehicle.
However, when the uphill where the subject vehicle may move backward is estimated as a flat road, there is problem in that the subject vehicle moves backward when the vehicle stops or starts. When an appropriate inter-vehicular distance is not ensured between another subsequent vehicle and the subject vehicle, there is a problem in that it is difficult to prevent a collision between the subject vehicle and another vehicle.
In addition, in the following traveling control device according to the related art, since the road surface gradient is detected after the stopped subject vehicle actually starts to move, it is not possible to prevent an inappropriate movement such as a backward movement of the subject vehicle. As a result, it is not possible to improve the estimation precision of the road surface gradient.
The present invention was made to solve the problems, and an object thereof is to provide a vehicle gradient estimating device and a vehicle traveling control device which are capable of performing an appropriate traveling control in accordance with a gradient estimation result by improving estimation precision of a gradient of a road being traveled.